This invention generally relates to the gasification of coal with an inert heat transfer medium (IHTM). More particularly, this invention is concerned with improvements in the processing of the ash, char and IHTM remaining after the gasification of coal.
Coal may be gasified using steam and hot IHTM solids. The particular details of the coal gasification reaction form no part of this invention and a detailed description of this reaction is not required.
The coal gasification reaction produces a mixture of ash, unreacted char and IHTM. This mixture is generally fed to a fluidized combustor or lift pipe. In the lift pipe combustor, the unreacted char is burned and the heat of combustion reheats the IHTM in the mixture. The reheated IHTM is recycled back to the coal gasifier. This system for burning the unreacted char and reheating the IHTM has several shortcomings. For example, it is difficult to size a lift pipe system for complete combustion of the unreacted char. Char combustion temperatures may fuse the free ash and cause slugging and agglomeration of the ash and IHTM, and may cause depositions on the lift pipe walls which could change the operating characteristics of the lift pipe or plug it. The fluidizing lift gas is heavily laden with solids causing hydrodynamic instability and sensitivity to gas rates, gas to solids ratios, and particle sizes. Moreover, char combustion produces a hot dirty gas containing carbon monoxide which is difficult to handle. Fluidizing a mixture of ash, char, and IHTM also causes erosion problems.
It is an objective of this disclosure to provide a method of burning unreacted char and reheating IHTM in a way that lessens or overcomes the problems encountered in fludized ash, char, IHTM combustors, allows for the storing of heat energy, and provides better combustion of the unreacted char remaining after a coal gasification reaction.